Process for protecting ferrous metal surfaces by coating and dipping solution for use therein



PROCESS FOR' PROTECTING FEKROUS METAL SURFACES BY, COATING' AND DIPPING- SOLUTION FOR USE TH'EREIN Charles W; -C1ark;..Westmount,- Quebec, and J ohn- H. Schloen; Montreal, Quebec, Canada, assignors. to Canadian Copper. Refiners Limited, Montreal 'East, Quebec, Canada, a corporation. of Canada OFFICE.

No Drawing; Application :Februar-yX'Z; .1949, Serial-rNo. 74;2 56-T- 1'5Claims: (Cl. 148 617) 1" 2 Ourtpresent. invention. relates to a-process of cheap methoduof protecting ferrous metal surprotecting ferrous metal.surfacesland adipping, facesandbeing.quiteefiective against corrosion,

solution. for. usev therein,.and more. particularly whethenthe surfacesv are further protected by a to .such'aprocess. and solution. which will provide: layerofpaint orilacquer or not. The provision: at protectivecoating for..iron andsteel surfaces ofisuchaz-novel.process is a primary object of to prevent or. substantially to. retard. corrosion our present invention,

thereof, such as-wouldbe occasioned byexposure: Further. objects .andadvantages of the present."

ofthemetal:tohighlycorrosive influences, such invention-Will appear from the followingspecifias seawater, whether the surfaces are further cationwhere-inthe invention is set forth in detail protected ,by-paint-or lacquer coatings or not 10,. and will-bepointed out in the-appended claims.

The present. invention.- is at continuation-im- Theinvention essentially consists in a novel. part of ourpriorandcopending application; Serial? dippingsolution and-process 'for the use thereof v No. 676,122, filed..June-. 11', 1946;.now' abandoned, in which articles-=of-the typedescribed may behaving thevsame title and is intended as a-subimmersed after cleaningand whichwill provide stitute. therefor.- As. such,..the*present" applica- 15sa:coating safiording the desired corrosion resisttion :includescertain numerical limitsof concening characteristicss If desired, however, prior to trations not included specifically? in said prior the. immersion otthe articles in the clipping soluapplication. This prior applicationisa continuafi m, w ch p c y: forms t OV b V tio-n-inspart o-f an .earlier.v application, which was mattenofithepresent invention; the articles may copendingtherewith andwhich isnowwabancloned, bepre-di-pped inanaqueous solution of potassium this earlier applicationvvvas:Serial.-No. 528,357, titaniumoxalatet This step. is optional in charfiledMarch 2'7, 1944, .and entitledProcession aeter, but-has-certaindesirable advantageous reprotecting metal surfaces-. sultsin some instancesr Many, attempts have-sheen made in the: past, Theadippingl-sol-ution of the present invention with more or less success, to provide coatin-gsq is aqueous in characterandmay be prepared by formetallic surfaces,- particularlythosew'ofiron; introducing n oa er' hreeba c jor and-steel articles; which-will protect saidsurfacese gradients;- Which will be hereinafter considered. aga-in s.corrosion.. someofrthese processes-have in-.detail asto.theircharacten composition andbeen. known under? the:- conventional names of other, requirements, these ingredients being (1): parkerizing-" and.-bonderizing." Many; of these "'=-a selenium compound-which is selected'from the processes have-used; alone-or irrcombination with. groupl-w-hichwconsists of selenium dioxide, seleniother. materials, a d-ippingsolution including.- ous acidanda-the alkali 'saltsthereof, and selenic' phosphoric acid; In substantially alLthese procacid and the alkali salts-thereof; (2) a zinc com-- esses.-the first step-hasbeen to clean the-metal pound whichtisselected from the group which in some suitable way. This-:is found 'to be neces- ;:consists oilzincoxide, zincselenite, zinc selenate,

sary also in accordance withthepresent-process,. phosphate: and zinc-chromium selenate:

the.cleaning-beingsefiectedrin'anyisuitablerway, (CrzGSeGrh-ZnC'rOr) and (3) phosphoric acid.

including. mechanical, cleaning; to; removesrusty, The severalingredients-will now be discussed in.

andscale and also-chemical cleaning whi-chmay f detail-l furthenbe dividedsintoctwoparts; first; that byr 40, Selenium compound:Underordinary circum--- theuse of acids and/oralkal-is to =remove-certain stances; it is preferred to useselenium dioxide as undesired. materials:solubl'erinone or thezot'herw thecselen-ium'compound in this'case'. However,

of .these two types of materials 'anel second by thec there may. alternatively: be used selenious or useof organic solvents forl-dissolvingi'org-anic im; selenic acids: or mixtures of such acids and/or purities and materials-,such as oil or grease; whiclrra their alkali salts, for exampla'mixtures of sodium are soluble in,-such solventsp This portion of-= selenite--(NazSeO3') with selenic acid (H2SeO4'),

the process.-- is includedsmerely, aseoneessential; or -even-mixtures of alkali salts 'of the two selenium stepof the process, but will-. notberfurtherfdis acids-named; such as sodiumselenite and" sodium cussed :in .detail herein-r selenate;

While. some of. the zpriort processes above -re The :-concentration 'of' the selenium compound: ferredttohave.been-considered.reasonablyefiec in the solution is preferably'calculated as SeOz,"

tive. for certainrpurposes, wexhavevfoundl-thats the-ricalculation"preferably-also including all the particularly good'xresultswareiobtainable: by; fol-' seleniummpresentir'rv the solution: irrespective of lowing the process hereinaiterr-describedsimdes hovw'itsz'is'.introduced: onthisbasis, th'e' limits tail this processraffordingra;relativelysimplerandz; 5 contemplatdwareirom about 1 to I about 300* grams per liter as extreme limits, with a concentration of about 200 grams per liter preferred. It has been found in this connection that higher concentrations of this ingredient give heavier coatings. The time required to produce a desired weight of coating is shorter with higher concentrations of this ingredient. The temperature, as hereinafter set forth, is not particularly critical, but is usually affected by concentration in the sense that to get a given result, a lower temperature may be used with higher concentration and vice versa.

Zinc compound-While several such compounds have been tried and found to be successfully operative, as aforesaid, it is preferred to use zinc oxide (ZnO) because of its relative cheapness and availability. Alternatively, however,

zinc selenite, zinc selenate and zinc phosphate zinc phosphate as affecting the concentration of phosphoric acid. The compound zinc-chromium selenate, the formula of which is given above, has been used with somewhat less desirable results than with zinc oxide; but it is still effective to get satisfactory results for some purposes and may for certain particular uses be even more desirable. It is, therefore, to be considered within the purview of the present invention.

The concentration desired for this ingredient is calculated on the basis of zinc oxide by the usual manner of calculation of equivalents. On this basis it has been found that concentrations from about 10 grams per liter to about 250 grams per liter will be effective to produce desirable results. The preferred concentration is about 100 grams per liter of zinc oxide or its equivalent of other compounds. It has been found, however, that zinc chloride, Zinc nitrate and zinc sulphate do not give desirable results, probably for the reason that these compounds are too highly ionized.

The temperature and time factors as to their effect upon or the manner in which they are affected by the zinc compound is similar in character and direction to those stated above in connection with the selenium compound ingredient.

Phosphoric acid.-This ingredient has no equivalents as far as We have ascertained up to this time. The concentrations required for use are preferably relatively high. There should be at least an effective amount present, i. e., enough to accomplish the objects of providing a satisfactory coating, and second, that there shall be enough phosphoric acid present to dissolve all the zinc compound, such as ZnO, present in accordance with the teachings given above. As such it has been found that the concentration of phosphoric acid present, calculated as H3PO4, should be from about 40 to about 500 grams per liter. The preferred concentration of phosphoric acid is about 300 grams per liter.

It has been found that as a rather rough general rule, the clipping time is inversely proportional to the concentration of phosphoric acid, which is another reason why a relatively high concentration is desired, so that the time may be reduced to a practicable value.

Temperature.--The temperature at which the bath is maintained during the dipping operation is not particularly critical. Dipping at room temperature is substantially as effective in producing a satisfactory coating as the use of higher temperatures. It is desired, however, to maintain the dipping solution below its boiling point so as to maintain the concentration thereof in a desired range and prevent loss of the ingredients, as well as to prevent such discomfort to personnel working nearby, as might be occasioned by the vaporization of substantial amounts of some of the ingredient materials aforesaid. On the other hand, it has been found that higher temperatures permit the operations to take place in a shorter time, so that it is usually desired to maintain the temperature of the dipping bath in the range between about C. and the boiling point of the solution.

Time of immersion.-This factor is determined principally by other factors. The primary consideration is the thickness of the coating which is to be formed on the article in question, longer times giving greater thickness. Also, as above indicated, the time is to a certain extent a function of the temperature of the bath, so that with higher temperatures, shorter times may be used to effect the same result. The time is also a function of the concentrations used as aforesaid, higher concentrations within the limits given being effective to reduce the time required to attain any given result. An example of a time actually used can be given in that a satisfactory coating may be applied in about 30 minutes with the dipping solution of the preferred composition as aforesaid at room temperature and a coating formed which will be reasonably effective even against corrosion by a 3% salt solution. With the same time of dipping, a coatin of increased thickness may be formed using the same solution, but at a temperature approaching boiling point, the increased thickness giving an increased time of protection before corrosion, sometimes as much as severalfold. A 10% to 15% increase in protection time may, however, be expected by increasing the temperature to near the boiling point with the same dipping time,

Added material.It has been found that certain organic materials may be added as minor ingredients to the dipping bath to give a superior type of coating. The one particularly referred to at the present time, and herein specifically claimed, is glycollic acid, which is preferably added to the bath in a concentration of about one gram per liter. The outside limits for this ingredient are, however, from about 0.1 (1 or 2 drops) to about 50 grams per liter. These materials act in a way to give a superior type of coating, preferably one which more uniformly coats the iron or steel article.

The particular mechanics of the reaction are unknown, but the following facts have been found in respect thereto. These materials are not catalysts in the true sense, since they are apparently consumed in the coating process and must be replenished. It is possible that they are adsorbed on the surface of the articles to be coated somewhat like addition agents in electrolysis. Another theory which has been advanced is that these materials act similar to de-polarizing agents in that they break up the hydrogen evolved from the attack on the iron by the phosphoric acid, so as to permit the coating to be more uniformly deposited and hence the coating tends to prevent corrosion for a longer period than if the addition agents were not added. In any event, we do not wish to be limited by any of the theories here advanced, but merely prefer to rely upon the claims as presented, broadly construed. While "we have disclosed but one such addition agent specifically, and merely claimed that one, claims which do not include this one addition agent are intended to be construed so as to cover the use of any such material found to be effective in this manner, including the glycollic acid herein particularly disclosed and also to cover the dipping solution without any such agent.

Character of the cocting.-The exact chemical composition of the coating produced as aforesaid is not known. It is believed to contain selenium and zinc, and probably also the P04 radical insome combination. The coating is very light in weight, probably in the order of magnitude of .001 to .002 gram per square inch of surface coating. The chemical reactions incident to forming the coating are also not known although it is believed that the surface of the ferrous article is attacked in some way by the phosphoric acid with the evolution of some hydrogen and that there is some chemical interchange and/or deposit of either selenium or zinc or compounds of one or both of these materials therein. In any event, the exact character of the coating and the reactions by which it is formed are not herein depended upon in support of the patentability of the claims, which are directed to the process by which it is formed and to the clipping solution composition per se.

Further process detaiZs.In the ordinary practice of the process, the iron or steel article may be cleaned, for example by first dipping in a hot solution of sulphuric acid for about a minute, or alternatively by electrolysis in cold sulphuric acid, then washed in water and dried. The article may then be washed in carbon tetrachloride to remove grease and dried, then optionally dipped in potassium titanium oxalate. It may in some instances, however, be desirable not to dry the article between the steps of pickling and/or cleaning in an organic solvent and the dipping, as cleaned ferrous articles are highly susceptible to corrosion, which may be effectively prevented by dipping them into the solution of the present invention immediately after the cleaning and without an intervening drying step.

As a result of the practice of the preferred embodiment of the invention, including the preferred composition for the dipping bath as above set forth and including the use of glycollic acid as an addition agent, a control panel cleaned as aforesaid was immersed in a 3% solution of NaCl and was found to rust in about 16 hours. This panel had not been treated in accordance with the present invention. As compared to this, a similar panel, treated in accordance with the present invention, with the dipping solutiona't room temperature, was also exposed to a similar concentration of salt water and was prevented from rusting by the coating applied theretofor 408 hours. A corresponding panel, to which the coating was applied at a temperature near the boiling point, lasted 456 hours before the first appearance of rust thereon, when exposed to the same 3% NaCl solution.

While we have disclosed herein the preferred embodiment of our invention and certain alternatives now known to us which will be effective to produce desirable results, we do not Wish to be limited except by the appended claims, which are to be construed validly as broadly as the state of the prior art permits.

What is claimed is:

1. The process of protecting the surfaces of ferrous metal articles, which comprises the steps of cleaning the surfaces of the metal to be protected; and immersing the cleaned articles, for a time predetermined in accordance with the thickness of the coating to be formed thereon, in an aqueous solution, the essential active ingredients of which, per liter of solution, consist of: (a) at least one zinc compound selected from the group which consists (as introduced into said aqueous solution) of zinc oxide, zinc selenite, zinc selenate, zinc phosphate and zinc chromium selenate [CrzCSeOQaZnCrOr], and in such amount that the total concentration of zinc in the final solution, calculated as ZnO, will be about 10 to about 250 grams, (b) at least one selenium compound selected from the group which consists (as introduced into said aqueous solution) of selenium dioxide, selenious acid, the alkali salts thereof, selenic acid and the alkali salts thereof, and in such amount that the total concentration of selenium, in the final solution, calculated as SeOz, will be from about 1 to about 300 grams, and (c) phosphoric acid in a concentration of from about 40 to about 500 grams, and one which will be suflicient to dissolve all the zinc compounds present, said solution containing materials resulting from the simultaneous presence in aqueous solution of the ingredients aforesaid.

2. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, wherein the selenium present in said aqueous solution is in a concentration, calculated as SeO'z, of about 200 grams per liter.

3. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, wherein the zinc present in the aqueous solution is in a construction, calculated as ZnO, of about grams per liter.

4. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, wherein the selenium present in the aqueous solution is in a concentration, calculated as S602, of about 200 grams per liter, and wherein the zinc P present'in the aqueous solution is in a concentration, calculated as ZnO, of about 100 grams per liter.

5. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, wherein said selenium compound is introduced into the solution in the form of selenium dioxide.

'6. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, wherein said zinc compound is introduced into the solution in the form of zinc oxide.

7. The process of protecting the surfaces of ferrous metal articles in accordance with claim l, wherein said selenium compound is introduced into the solution in the form of selenium dioxide, and said zinc compound is introduced into the solution'in the form of zinc oxide.

8. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, wherein said selenium compound is introduced into the solution in the form of selenium dioxide, and the concentration of selenium in said solution, calculated as SeOz, is about 200 grams per liter, and wherein said zinc compound is introduced into the solution in the form of Zinc oxide, and is present in a concentration such as to give a concentration of zinc, calculated as ZnO, of about 100 grams per liter.

9. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, comprising the additional step, to be performed after the cleaning and prior to the immersion as aforesaid, of predipping the metal articles to be treated in an aqueous solution of potassium titanium oxalate.

10. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, comprising the additional step of maintaining said aqueous solution in a temperature range between about 90 C. and its boiling point during the immersion therein of metal articles to be treated.

11. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, wherein said aqueous solution contains as an additional active ingredient, glycollic acid, in a concentration of this ingredient of about 0.1 to about 50 grams per liter.

12. The process of protecting the surfaces of ferrous metal articles in accordance with claim 1, wherein said aqueous solution contains, as an additional active ingredient, glycollic acid in a concentration of this ingredient of about one gram per liter.

13. The process of portecting the surfaces of ferrous metal articles, which comprises the steps of cleaning the surfaces of the metal to be protected; and immersing the cleaned articles, for a time predetermined in accordance with the thickness of the coating to be formed thereon, in an aqueous solution, the essential active ingredients of which, per liter of solution, consist (as introduced into the solution) of (a) selenium dioxide in an amount sufficient to provide in said solution a concentration of selenium, calculated as SeOz, of about 200 grams, (1)) zinc oxide in an amount sufficient to provide in said solution a concentration of zinc, calculated as ZnO, of about 100 grams, phosphoric acid in an amount to provide in said solution a concentration, calculated as H3PO4, of about 300 grams, and (d) glycollic acid in an amount sufiicient to provide in the final solution a concentration of about one gram, said solution containing materials resulting from the simultaneous presence in aqueous solution of the ingredients aforesaid, and maintaining the temperature of the solution during the immersion of metal articles therein in the range of about 90 C. to the boiling point of the solution.

14. A dipping solution for protecting cleaned metal surfaces, said solution being an aqueous solution, the essential active ingredients of which, per liter of solution, consist of: (a) at least one zinc compound selected from the group which consists (as introduced into said aqueous solution) of Zinc oxide, zinc selenite, zinc selenate, zinc phosphate and Zinc chromium selenate [CI'2(S804)3.ZHC1O4], and in such amount that the total concentration of zinc in the final solution, calculated as ZnO, will be about to about 250 grams, (b) at least one selenium compound selected from the group which consists (as introduced into said aqueous solution) of selenium dioxide, selenious acid, the alkali salts thereof, selenic acid and the alkali salts thereof, and in such amount that the total concentration of selenium in the final solution, calculated as SeOz, will be from about 1 to about 300 grams, and (c) phosphoric acid in a concentration of from about 40 to about 500 grams, and one which will be sufiicient to dissolve all the zinc compounds present, said solution containing materials resulting from the simultaneous presence in aqueous solution of the ingredients aforesaid.

15. A dipping solution for protecting cleaned ferrous metal surfaces, said solution being an aqueous solution, the essential active ingredients of which, per liter of solution, consist (as introduced into the solution) of: (a) selenium dioxide in an amount sufficient to provide in said solution a concentration of selenium, calculated as SeOz, of about 200 grams, (1)) zinc oxide in an amount sufiicient to provide in said solution a concentration of zinc, calculated as ZnO, of about 100 grams, (0) phosphoric acid in an amount to provide in said solution a concentration, calculated as HsPO4, of about 300 grams, and (d) glycollic acid in an amount sufficient to provide in said solution a concentration of about one gram, said solution containing materials resulting from the simultaneous presence in aqueous solution of the ingredients aforesaid, and maintaining the temperature of the solution during the immersion of metal articles therein in the range of about C. to the boiling point of the solution.

CHARLES W. CLARK. JOHN H. SCHLOEN.

REFERENCES CITED The following referen'ces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,359,972 Edison Nov. 23, 1920 1,961,030 Bengough et a1 May 29, 1934 2,066,611 Christy Jan. 5, 1937 2,067,214 Tanner et al Jan. 12, 1937 2,067,216 Thompson et al. Jan. 12, 1937 2,186,085 Wein Jan. 9, 1937 2,303,350 Fuller Dec. 1, 1942 2,400,573 Prutton May 21, 1946 OTHER REFERENCES Lange, Handbook of Chemistry, 6th Edition, 1946, page 276, published by Handbook Publishers, Inc., Sandusky, Ohio.

W. H. Banks, Journal of the Chemical Society (London) 1934, pages 1010 to 1012.

Certificate of Correction Patent No. 2,475,944 July 12, 1949 CHARLES W. CLARK ET AL. It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 3'7, for the Word construction read concentration; column 7, line 24, for portecting read protecting;

and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 20th day of December, A. D. 1949.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents. 

